The present invention relates generally to electricity meters. More specific, the present invention relates to electricity demand meters with load profile recording capability.
Electricity meters are well known. These meters can be electromechanical based meters whose output is generated by a rotating disk, electronic based meters whose output component is generated electronically, and hybrid meters which use an electronic register in combination with a rotating disk. Electronic registers are in common use today with induction type watthour meters. Typically the induction type watthour meter contains a pulse initiator which senses rotation of the meter disc and provides pulses proportional to energy consumption to the register. Optical sensors for detecting rotation of the meter disc which provide pulses proportional to energy consumption to the register are also known. These electronic meters are typically used for the measurement of kilowatt demand and/or time of use (TOU) energy consumption. In electricity metering, electric utility companies historically have found it desirable to measure, in addition to total kilowatt-hours (real volt amperes), power factor, KVA, or reactive volt amperes.
The aforementioned demand meters only measure kilowatt, KQ, Kvar, or KVA demand. Demand calculations are determined by rolling, block or thermal demands. A rolling demand calculation allows the interval used for calculating demand to be subdivided into even subintervals. The demand calculation is then made at the end of each subinterval. Block demand is a special case of rolling demand where the block demand interval equals one subinterval of the rolling demand calculation. Thermal demand is the thermal measurement of kilowatts or KVA. The electronic meters utilizes an algorithm to emulate this thermal measurement. Regardless of which demand calculation is made, the maximum demand is typically continuously displayed by the meter.
The aforementioned TOU meters also calculate kilowatt demand. However, TOU meters also keep time and date information, and a rate schedule. The electricity is metered in accordance with the rate schedule for different time periods and days.
The electronic demand and TOU meters are well known in the art. Further, in order to accumulate data representative of these types of consumption, a time base is usually required with both meter types. This time base is used for interval timing of typically 5, 15, 30 or 60 minutes for calculation of kilowatt demand and for keeping time and date information in time of use meters.
For a detailed description pertaining to electricity metering and in particular for detailed information pertaining to the various types of electrical services and distribution systems and the types of meters utilized to perform kilowatt-hour, varhour and Qhour metering, reference is made to the Handbook for Electricity Metering, Eighth Edition, published by the Edison Electric Institute.
Load profile recording has been applied to TOU meters, whereby energy consumption is recorded (i.e., stored) in discrete time intervals. The recording of this information allows the user to analyze electricity use and modify usage to take advantage of lower rate time periods. Again the time periods and rates are defined in the stored rate schedule in the TOU meter. This method of recording usage in discrete time intervals requires the user to back track the time of usage in the discrete time intervals from the time recorded information was accessed.